Acrylonitrile polymer composition stabilized with metal formaldehyde sulfoxylate and formaldehyde and method of making same



ACRYLONITRILE POLYMER COMPOSITION STA- BILIZED WITH METAL FORMALDEHYDESUL- FOXYLATE AND FORMALDEI-IYDE AND METI-I A OD OF MAKING SAME Lloyd T.Jenkins, Decatur, Ala., and Richard R. Holmes,

Bethesda, Md., assignors to The Chemstrand Corporation, Decatur, Ala, acorporation of Delaware No Drawing. Application May 23, 1956 Serial No.586,678 t 1 Claims. (onto-32.6

This invention relates to the stabilization of acrylo: nitrile polymersand blends thereof. More particularly, it relates to the stabilizationof acrylonitrile polymers and blends thereof which have a tendency todevelop color upon standing or application of heat. The term polymer, asemployed in the instant description and claims, is intended to includehomopolymers, copolymers, and blends thereof, said polymers containingat least 80 percent by weight of polymerized or copolymerizedacrylonitrile in the polymer molecule.

vAcrylonitrile polymers containing 80 percent or more of acrylonitrileare generally insoluble in the more common solvents. In those instanceswhere suitable sol ventsihave been found, in order to effect solution,the

application of heat is usually necessary. Where heat is employed toeffect solutions, from which shaped articles are to be formed, a tan todark brown color frequently develops in the solutions and therefore iscarried over into the product formed therefrom. This color also develops in solutions upon standing for prolonged periods of time.

The mechanism which causes color formation has not been definitelyascertained, although a variety of reasons therefor have been advanced.The presence of metal ions, such as iron, copper and manganese in thesolutions may, cause the color. The employment of amide compounds assolvents may result in formation of amines when heat is applied andcause color in the compositions. Impurities present in the solvents havealso been cited as a cause. Whatever may be the reasonfor colorformation; it results in compositions and products of undesirpractisingthe instant invention are those having the generic formula,

i I R O-'M in which R is an alkanol group containing 1 to 3 carbonatoms, an acyl group containing 1 to 3 carbon atoms or an aryl groupcontaining 6 to 8 carbon atoms, n is an integer from 1 to 2, and M issodium, potassium, zinc, etc. formaldehyde sulfoxylate, zincformaldehyde sulfoxylate,"

potassium formaldehyde sulfoxylate, zinc acetaldehyde" sulfoxylate,sodium acetaldehyde sulfoxylate, potassium' acetaldehyde sulfoxylate,zinc propionaldehyde sulfoxy late, sodium propionaldehyde sulfoxylate,potassium prof be present in a small amount compared to the amount ofable standards and. therefore, has been the source of K concern,particularly in commercial operation where such types of polymers orcopolymers are employed.

Accordingly, it is an object of the present invention to preventundesirable color formation in acrylonitrile polymer compositions.Another object is to minimize color formation when solutions of theacrylonitrile polymers are permitted to stand for a prolonged period oftime or upon application of heat. t

It is also an object of the invention to prevent color formation inacrylonitrile polymers at elevated temperatures. A still further objectof the invention is the production ,of solutions of acrylonitrilepolymers and articles propolymer dissolved. Thus, although the amount isnot critical, it is preferred that the inhibiting agent be present inthe amount of about 0.3 to 3 percent, based on the total weight of thepolymer. The inhibiting agent may be added to the solvents before orafter the polymer is dissolved therein. The inhibiting agent permitsexposure to high temperatures for prolonged standing periods without thedevelopment of the objectionable color which usually results in suchsolutions. The compositions of the instant invention may be prepared ina varying temperature range. For example, the compositions of theinstant invention may be prepared by mixing the polymer, a suitablesolvent and the inhibiting agent at any temperature or heating themixture to a temperature up to the boiling point of the solvent.

Among the solvents which may be used in practising the instant inventionare N,N-dimethylformamide, N,N'- dimethylacetamide, aqueous zincchloride, sulfuric acid, aqueous nitric acid, aqueous sodiumthiocyanate, "ethylene carbonate, sulfolane, nitromethane, etc.

The polymeric materials, which may be employed in the practice of thepresent invention, are polyacrylonitrile, copolymers, including binaryand ternary polymers containing at least 80 percent by weight ofacrylonitrile in the polymer molecule, or a blend comprisingpolyacrylonitrile or copolymers comprising acrylonitrile with from 2 to50 percent of another polymeric material, the blend having an overallpolymerized acrylonitrile content of at least 80 percent by weight.While the preferred polymers employed in the instant invention are.duced therefrom having improved color characteristics 3 Other objectsand advantages will be apparent froma consideration of the descriptionof the invention which follows hereafter.

"In general, the objects of the invention are accomplished by dissolvingthe polymer of acrylonitrile in a suitable solvent therefor andpreventing or minimizing color ,.formation by the presence in thesolution as an inhibiting L'agent, a combined reagentcomprisingqanorganic metal "shlfoxylate and formaldehyde.

Among the sulfoxylates which'may' be employed intxl;

those containing at least percent of acrylonitrile, generally recognizedas the fiber-forming acrylonitrile poly.- mers, it will be understoodthat the invention is likewise applicable to polymers containing lessthan 80 percent acrylonitrile and the same stability is realized withthe inhibiting agents defined herein. The acrylonitrile poly'- .of'another monomer containing the C=C linkage and copolymerizable withacrylonitrile. "Suitable mono- Compounds illustrative of this classare'sodium' ,3. olefinic monomers include acrylic, alpha-chloroacrylicand methacrylic acids; the,.,acrylates, such as methylmethacrylate,ethylmethacrylate, butylmethacrylate, methoxymethyl :methacrylate,'beta-chloroethyl methacrylate, and the corresponding esters of acrylicand alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinylbromide, vinylidene chloride, l-chloro l bromoethylene;methacrylonitrile; acrylamide and methacrylamide;alpha-chloroacrylamide, or monoalkyl substitution products thereof;methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinylchloroacetate, vinyl propionate, and vinyl stearate; N-vinylimides, suchas N-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters;itaconic acid and itaconic ester; N-vinylcarbazole; vinyl furane; alkylvinyl esters; vinyl sulfonic acid; ethylene alpha, beta-dicarboxylicacids or their anhydrides or derivatives, such as diethylcitraconate,diethylmesaconate, styrene, vinyl naphthalene;vinyl-substituted tertiaryheterocyclic amines, such as the'vinylpyridines and alkyl-substitutedvinylpyridines, for example, 2-vinylpyridine, 4-vinylpyridine,2-methyl-5-vinylpyridine, etc.; l-vinylimidazole and alkyl-substitutedl-vinylimidazoles, such as 2-, 4-, or 5 methyl-l-vinylimidazolc, andother C=C containing polymerizable materials.

The polymer may be a ternary interpolymer, for example, productsobtained by the interpolymerization of acrylonitrile and two or more ofany of the monomers, other than acrylonitrile, enumerated above. Morespecifically, and preferably, the ternary polymer comprisesacrylonitrile, methacrylonitrile, and 2-vinylpyridine. The ternarypolymers preferably contain from 80 to 97 percent of acrylonitrile, from1 to percent of a vinylpyridine or a l-vinylimidazole, and from 1 to 18percent of another substance, such as methacrylonitrile or vinylchloride.

The polymer may also be a blend of polyacrylonitrile or of a binaryinterpolymer of from 80 to 99 percent the sodium salts of other peroxyacids, and any other water-soluble compound gontaining a peroxy group(OO-). A wide variation in the quantity of peroxy compound is possible.For example, from 0.1 to 3.0 percent by weight of the polymerizablemonomer may be used. The catalyst may be charged at the outset of thereaction, or it may be added continuously or in increments throughoutthe reaction for the purpose of maintaining a more uniform concentrationof catalyst in the reaction mass. The latter is preferred because ittends to make the resultant polymer more uniform in its chemical andphysical properties.

Although the uniform distribution of the reactants throughout thereactionmass can be achieved by vigorous agitation, it is generallydesirable to promote the uniform distribution of reagents by using inertwetting agents, or emulsion stabilizers. Suitable reagents for this pur-M pose are the water-soluble salts of fatty acids, such as sodium oleatcand potassium stearate, mixtures of watersoluble fatty acid salts, suchas common soaps prepared by the saponification of animal and vegetableoi1s, the amino soaps, such as salts of triethanolamine and (lode?cylmethylamine, salts of rosin acids and mixtures thereof, thewater-soluble salts of half esters of sulfuric acid and long chainaliphatic alcohols, sulfonated hydrocarbons, such as alkyl arylsulfonates, and any other of a wide variety of wetting agents, which arein general organic compounds containing both hydrophobic and hydrophilic radicals. The quantity of emulsifying agents will depend uponthe particular agents selected, the ratio of monomer to be used, and theconditions of polymerization. In general, however, from 0.01 to 1.0percent by a weight of the monomers may be employed.

acrylonitrile and from 1 to 20 percent of at least one i other C=Ccontaining substance with from 2 to 50 percent of the weight of theblend of a copolymer of from 10 to 70 percent of acrylonitrile and fromto 90 percent of at least one other C=C containing polymerizablemonomer. meric material comprises a blend, it will be a blend of acopolymer of 90 to 98 percent acrylonitrile and from 2 to 10 percent ofanother mono-olefinic monomer, such as vinyl acetate, which is notreceptive to dyestuff, with a sufiicient amount of a copolymer of from10 to 70 percent of acrylonitrile and from 30 to 90 percent of avinyl-substituted tertiary heterocyclic amine, such as vinylpyridine orl-vinylimidazole, to give a dyeable blend having an overallvinyl-substituted tertiary heterocyclic amine content of from 2 to 10percent, based on the weight of the blend.

The polymers, useful in the practice of the present invention, may beprepared by any conventional poly- Preferably, when the polymerizationprocedure, such as mass polymerization methods, solution polymerizationmethods, or aqueous emulsion procedures. However, the preferred practiceutilizes suspension polymerization wherein the polymer is prepared infinely divided form for immediate use in the fiber fabricationoperations. The preferred suspension polymerization may utilize batchprocedures, wherein monomers are charged with an aqueous mediumcontaining the necessary catalyst and dispersing agents. A moredesirable method involves the semi-continuous procedure in which thepolymerization reactor containing the aqueous medium is charged with thedesired monomers and the continuous withdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any water- The emulsionpolymerizations are preferably conducted in glass or glass-lined vesselswhich are provided witha means for agitating the contents. Generally,rotary stir ring devices are the most effective means of insuring theintimate contact of the reagents, but other methods may be successfullyemployed, for example by rocking or tumbling the reactors. Thepolymerization equipment generally used is conventional in the art andthe adapt-a tion of a particular type of apparatus to the reactioncontemplated is within the province of one skilled in the art. Thearticles manufactured therefrom may be produced by well-knownconventional methods, for example, the wet-spinning, dry-spinning andmelt-spinning methods for producing fibers.

The following examples are illustrative rather than limitative and 'allparts, proportions and percentages are by weight unless otherwisespecified.

EXAMPLE I 7.5 grams of a polymer blend of 88 percent of a'copolymercontaining 94 percent of acrylonitrile and 6 percent of vinyl acetateand 12 percent of a copolymer of 50 percent of acrylonitrile and 50percent of Z-methyl- S-vinyl pyridine were added to 45 milliliters ofN,N- dimethylacetamide containing approximately 0.05 gram of titaniumdioxide. The mixture was stirred and heated to 70 C. It was then quicklycooled to room temperature and the color measured. This sample was usedas a control. The purity is set forth below. Subsequently, like sampleswere prepared but with 0.150 gram of a color inhibitor containing 0.075gram each of sodium formaldehyde sulfoxylate and formaldehyde. Thepurity is set forth below.

Table l Percentage Purl Used via an EXAMPLE II p 7.5 grams of acopolymer containing 94 percent of acrylonitrile and 6v percent or vinylacetate were added to 45 milliliters of N,N-dimethylacetamide containingapproximately 0.05 gram of titanium dioxide. The mixture was stirred andheated for 35 minutes at 70 C. It was then quickly cooled to roomtemperature and the color measured. This sample was used as a control.The purity is set forth below. Subsequently, like samples were preparedbut with 0.150 gram of an inhibiting agent containing 0.075 gram each ofsodium formaldehyde sulfoxylate and formaldehyde; The purity is setforth below.

Table II Inhibitor Percentage Purity Used Control 10. 2 SodiumFormaldehyde Sulloxylate and Formaldehyde 2 4. 8

EXAMPLE III 7.5 grams of an acrylonitrile homopolymer were added to 45milliliters of N,N-dimethylacetamide containing approximately 0.05 gramof titanium dioxide. Themixture was stirred and heated for 50 minutes at90 C. It was then quickly cooled to room temperature and the colormeasured. This sample was used as a control. The purity of the controlsample is set forth below. Subsequently, like samples were prepared butwith 0.150 gram of an inhibiting agent containing 0.075 gram each ofsodium formaldehyde sulfoxylate and formaldehyde. .The purity is setforth below;

Table III Inhibitor Percentage Purity Used Control 8. 5 SodiumFormaldehyde Sulfoxylate and Formaldehyde 2 2.8

The tests for color indicative of approaching whiteness used throughoutthe examples consist of measurements of purity as calculated from thetristimulus values determined on a General Electric spectrophotometer bythe methods recommended by the Standard Observer and Coordinate Systemofthe International Commission on Illumination, as fully set forth in theHandbook of Colorimetry published by The Technology Press, MassachusettsInstitute of Technology in 1936. 3

The compositions of the instant invention present many advantages. Forexample, products formed from the polymer solutions of the instantinvention are free of objectionable color and therefore of greatercommercial value. In preparing the polymer solutions, heat may beapplied without the danger of color formation and the solutions, ifnecessary, may stand for prolonged periods and remain free of color. Theinhibiting agents are readily available and inexpensive. Therefore, nogreat increase in production cost is necessary. The compositionscontaining the inhibitors may be prepared without going through detailedand elaborate procedures that necessitate expensive changes in thedesign of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparentlywidely different embodiments of this invention can be made withoutdeparting from the spirit and scope thereof. Accordingly, it is to beunderstood that this invention is not to be limited to the specificembodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer 6 containing? atleast percent of polymerized acrylo nitrile and up to 20 percent ofanother polymerizable mono-olefinic monomer copolymerizable therewith, a$01., vent therefor, and an inhibiting agent containing substantiallyequal proportions by weight of a compound having the general formula 0 la R. o M wherein R is a radical selected from the group consisting ofalkanol groups containing 1 to 3 carbon atoms, n is an integer from 1 to2, and M is a metal. selected from the group consisting of sodium,potassium and zinc; and formaldehyde.

2. A new composition of matter as defined in claim 1 wherein the polymeris a copolymer containing from 80 to 98 percent of acrylonitrile andfrom 2 to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith.

'3. A new composition of matter as defined in claim 1 wherein thepolymer is a blend of 80 to 99 percent of (A) a copolymer containing to98 percent of acrylo nitrile and 2 to 10 percent of vinyl acetate and 1to 20 percent of (B) a copolymer containing 10 to 70 percent ofacrylonitrile-and 30 to 90 percent of 2--methyl-5-vinyl pyridine. 4. Anew composition of matter as defined in claim I wherein the polymer ispolyacrylonitrile. r

5. A new composition of matter as defined in claim 1 wherein the.compound is sodium formaldehyde Slli foxylate.

6. A new composition of matter as defined in claim 1 wherein thecompound is potassium formaldehyde sulfoxylate.

7. A new composition of matter as defined in claim 1 wherein thecompound is zinc formaldehyde sulfoxylate.

8. A new composition of matter as defined in claim 1 wherein the solventis N,N-dimethylacetamiide.

9. A new composition of matter comprising a polymer blend of (A) acopolymer containing 90 to 98 percent of acrylonitrile and 2 to 10percent'of another polymerizable mono-olefinic monomer and (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of a vinyl substituted tertiary heterocyclic amine, said blendhaving an overall vinyl substituted wherein R is a radical selected fromthe group consisting of alkanol groups containing 1 to 3 carbon atoms, nis an integer from 1 to 2, and M is a metal selected from the groupconsisting of sodium, potassium and zinc; and formaldehyde.

10. A new composition of matter comprising a copolymer containing 80 to98 percent of acrylonitrile and 2 to 20 percent of vinyl acetate, asolvent therefor, and 0.3 to 15 percent, based on the total weight ofthe polymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of a compound having thegeneral formula,

wherein R is a radical selected from the group com sisting of'alkanolgroups containing 1 to 3 carbon atoms, n is an integer from 1 to 2, andM is a metal selected from the group consisting of sodium, potassium andzinc; and formaldehyde. 1 I

11. A new composition of matter comprising a polymer blend of 80 to 99percent of (A) a copolymer containing 90 to 98 percent of acrylonitrileand 2 to percent of vinyl acetate and 1 to 20 percent of (B) a copolymercontaining 10 to 70 percent of acrylonitrile and 30 to 90 percent of2-methyl-S-vinylpyridine, a solvent therefor, and 0.3 to percent, basedon the total weight of the polymer, of an inhibiting agent, saidinhibiting agent containing substantially equal proportions by weight ofa compound having the general formula,

0 r R 0--M |n wherein R is a radical selected from the group consistingof alkanol groups containing 1 to 3 carbon atoms, n is an integer from 1to 2, and M is a metal selected from the group consisting of sodium,potassium and zinc;

In wherein R is a radical selected from the group consisting of alkanolgroups containing 1 to 3 carbon atoms, n is an integer from 1 to 2, andM is a metal selected from the group consisting of sodium, potassium andzinc;

and formaldehyde.

13. A new composition of matter comprising polyacrylonitrile, a solventtherefor, and 0.3 to 15 percent, based on the total weight of thepolymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of a compoundhaving thegeneral formula,

wherein R is a radical selected from the group consisting of alkanolgroups containing 1 to 3 carbon atoms, n is an integer from 1 to 2, andM is a metal selected from the group consisting of sodium, potassium andzinc; and formaldehyde.

14. A method for preparing a new composition of matter comprising mixinga polymer containing at least 80 percent of polymerized acrylonitrileand up to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith, a solvent therefor, and an inhibiting agentcontaining substantially equal proportions by weight of a compoundhaving the general formula,

R OJ" wherein R is a radical selected from the group consisting ofalkanol groups containing 1 to 3 carbon atoms, 1: is an integer from 1to 2, and M is a metal selected from the group consisting of sodium,potassium and zinc; and formaldehyde and heating the mixture to form ahomogeneous solution.

15. The method as defined in claim 14 wherein the polymer is a copolymercontaining from 80 to 98 percent of acrylonitrile and from 2 to 20percent of another polymerizable mono-olefinic monomer copolymerizabletherewith.

16. The method as defined in claim 14 wherein the polymer is a blend of80 to 99 percent of (A) a copolymer containing 90 to 98 percent ofacrylonitrile and 2 to 10 percent of vinyl acetate and 1 to 20 percentof (B) a copolymer containing 10 to percent of acrylonitrile and 30 to90 percent of 2-methyl-5-vinyl pyridine.

17. The method as defined in claim 14 wherein the polymer ispolyacrylonitrile.

18. A method for preparing a new composition of matter comprising mixinga polymer blend of to 99 percent of (A) a copolymer containing to 98percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to20 percent of (B) a copolymer containing 10 to 70 percent ofacrylonitrile and 30 to 90 percent of 2- methyl-S-vinyl pyridine, asolvent therefor, and 0.3 to 15 percent, based on the total weight ofthe polymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of sodium formaldehydesulfoxylate and formaldehyde, and heating the mixture to a temperaturein a range of 25 C. to the boiling point of said mixture to form ahomogeneous solution.

References Cited in the file of this patent UNITED STATES PATENTS2,502,030 Scheiderbauer Mar. 28, 1950 2,688,008 Chaney et al. Aug. 31,1954 1 FOREIGN PATENTS 1,027,445 France Feb. 18, 1953

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST80 PERCENT OF POLYMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHERPOLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENTTHEREFOR, AND AN INHIBITING AGENT CONTAINING SUBSTANTIALLY EQUALPROPORTIONS BY WEIGHT OF A COMPOUND HAVING THE GENERAL FORMULA